A conventional bicycle essentially comprises a pedal structure, a gear train coupled to a wheel axis, and a chain connected between the pedal structure and the gear train. In general, the pedal structure has a crank shaft, a gear coupled to the crank shaft, and pedal cranks disposed at the two ends of the crank shaft, respectively, such that a cyclist treads on the pedals connected to the pedal cranks to thereby rotate the crank shaft, thus allowing the chain to drive the wheels of the bicycle to rotate.
To render cycling less laborious, the prior art discloses a bicycle which comprises a driving motor and a controller thereof so as for the driving motor to supply auxiliary power required for the rotation of a crank shaft coupled to a bicycle pedal structure. In this regard, a sensor is mounted on the crank shaft coupled to the bicycle pedal structure to thereby detect the rotation speed and torque of the crank shaft, so as to determine whether the controller is operating and determine whether to adjust the operating status of the driving motor.
Since the sensor is mounted on the crank shaft, it not only rotates together with the crank shaft but also transmits an electrical signal by coming into contact with a collector ring. As a result, the sensor is predisposed to poor contact with a collector ring and thus unstable transmission of the electrical signal. In addition, the overall structure is not only intricate but also vulnerable.